1. Field
The present disclosure relates to a system for preheating a fuel cell stack.
2. Description of the Related Art
Fuel cells have higher efficiencies and lower emissions than internal combustion engines, so fuel cells provide a promising alternative to internal combustion engines. Various types of fuel cells have been developed, for example, household fuel cells for supplying electricity to a home, car fuel cells for electric vehicles, small fuel cells for portable electronic devices, and the like.
Fuel cells convert a fuel directly into electricity. Fuel cells include a pair of electrodes, i.e., an anode and a cathode, and an electrolyte therebetween. Some fuel cells generate electricity and heat, by oxidizing a gaseous fuel, such as hydrogen, propane, methane, or the like.
A plurality of fuel cells (unit cells) may be assembled in a stack. The unit cells may include a membrane electrode assembly (MEA) and a bipolar plate. A membrane electrode assembly includes an anode electrode (also called a fuel electrode or an oxidation electrode) and a cathode electrode (also called an air electrode or a reduction electrode), and an electrolyte therebetween.
In this configuration, hydrogen ions that have moved to the cathode through the electrolyte membrane produce an electrochemical reduction reaction with oxygen supplied to the cathode. Accordingly, electric energy, reaction heat, and water are produced.
If a fuel cell is stopped in freezing conditions, water therein may be frozen. As a result, the fuel cell may fail to start and an MEA may be damaged by the expansion of the water.
In order to prevent the above problem, there is a method of removing water from the flow channels and the MEAs of a stack, by supplying a dry inert gas thereto. However, the method has a problem, in that a large amount of the inert gas must be supplied, for a long period of time, in order to sufficiently remove the water. In particular, while it is easy to remove the water from the channels of the bipolar plates, it is very difficult to remove the water from the MEAs.
In addition, another method involves preheating a stack using a heater. However, in this case, the melting of ice causes a reduction in the performance and life span of MEAs, because of volume changes that occur during the melting.
Another method involves filling the anode of a fuel cell with a solution having a low freezing point, such as methanol. However, in this case, the performance and life span of the fuel cell is decreased, because a platinum-based catalyst therein is poisoned with CO generated as a by-product of a chemical reaction between the platinum-based catalyst and the methanol. As a result, the shelf life of the platinum-based catalyst decreases, and the methanol that is not used in the reaction with the catalyst crosses over the electrolyte membrane from the anode to the cathode, resulting in cathode flooding.